<mat-form-field [formGroup]="fg">
  <mat-label>{{label}}</mat-label>
  <mat-select [multiple]="multiple" formControlName="{{key}}">
    <mat-option [value]="el.value" *ngFor="let el of options">{{el.label}}
    </mat-option>
    <mat-option *ngIf="!allLoaded && !loading ">
      <div #ghostRef>
        <mat-progress-spinner [color]="'primary'" [mode]="'indeterminate'" [diameter]="40">
        </mat-progress-spinner>
      </div>
    </mat-option>
  </mat-select>
</mat-form-field>